The book of "1 John" is a letter in the New Testament of the Christian Bible, traditionally attributed to the Apostle John. It addresses early Christian communities, emphasizing the importance of love, faith, and the nature of God. The letter encourages believers to live in accordance with their faith and to recognize the significance of Jesus as the Son of God. In "1 John," the author also warns against false teachings and encourages readers to remain steadfast in their beliefs. The themes of light versus darkness and the assurance of eternal life are central, highlighting the relationship between believers and God.